1. Field of the Invention
The present invention relates to a medical instrument for transdermally administering an ionic medicine used in the iontophoresis for permeating, into the living body, an ionic medicine useful for the living body by utilizing electrophoresis, and to a portable iontophoresis device by using the above medical instrument.
2. Description of the Related Art
The iontophoresis for permeating, into the living body, an ionic medicine useful for the living body by utilizing the electrophoresis, and has been widely known as a method of administering a medicine of a required amount into a diseased part in a pain-free state.
In the iontophoresis, a medicine-containing layer impregnated with an ionic medicine is placed on the living body, a working electrode is arranged on the side opposite to the living body with the medicine layer sandwiched therebetween, an counter electrode is placed on the living body separated away from the medicine-containing layer, and an electric current is permitted to flow across the working electrode and the counter electrode from a power source causing the ionic medicine to permeate into the living body. So far, this method has used a large device and could be practiced in particular places only such as in a hospital. In order to realize the iontophoresis at any time in any place, therefore, study has been forwarded vigorously concerning the iontophoresis devices that feature simple and compact structures and that can be carried.
The iontophoresis is a method of permeating an ionic medicine into the living body through the living body interface such as skin or mucous membrane. In this method, however, the ionic medicine does not necessarily pass through the living body interface but, conversely, it often happens that sodium cations, potassium cations and chloride anions permeate into the medicine-containing layer from the living body. In particular, ionic medicines that are believed to be useful for the living body have a smaller mobility than those of ions existing in the living body, and a desired medicine is not efficiently administered (does not efficiently permeate into the living body) in proportion to the amount of electricity that is supplied. A proposal has therefore been made to solve the above-mentioned problem by arranging an ion-exchange membrane that permits the passage of ions of the same polarity as the desired ionic medicine between the medicine-containing layer and the living body interface [see, for example, Prior Arts (A) and (B)].                Prior Art (A): International Patent Publication No. 504343/1991        Prior Art (B): Japanese Unexamined Patent Publication (Kokai) No. 98894/1996        
However, the iontophoresis device has problems in that the ionic medicine is decomposed on electrodes (working electrode and counter electrode) that are arranged for flowing a current, and water used as a solvent for the ionic medicine undergoes the electrolysis to form H+ ions and OH− ions that act on the living body to cause inflammation.
In order to solve these problems, a proposal has been made to further arrange an ion-exchange membrane between the medicine-containing layer and the electrode so that the ionic medicine contained in the medicine-containing layer will not come in direct contact with the electrode, and that H+ ions and OH− ions generated at the electrode will not migrate toward the living body [see, for example, Prior Arts (C) to (G)].                Prior Art (C): Japanese Unexamined Patent Publication (Kokai) No. 297277/1992        Prior Art (D): Japanese Unexamined Patent Publication (Kokai) No. 229128/2000        Prior Art (E): Japanese Unexamined Patent Publication (Kokai) No. 229129/2000        Prior Art (F): Japanese Unexamined Patent Publication (Kokai) No. 237328/2000        Prior Art (G): Japanese Unexamined Patent Publication (Kokai) No. 237329/2000        
FIG. 1 illustrates the structure of a representative working electrode part on a conventional iontophoresis device having a plurality of ion-exchange membranes. In FIG. 1, a medicine-containing layer 1 containing an ionic medicine is held in an outer cylinder 2, and an ion-exchange membrane 4 is provided on the side that comes in contact with the surface 3 of the living body for selectively permeating the ions of the same polarity as the pharmacologically effective ions of the ionic medicine. On the side that does not come in contact with the living body, on the other hand, there are arranged an ion-exchange membrane 5 for selectively permeating the ions of the polarity opposite to that of the pharmacologically effective ions of the ionic medicine, as well as an electrolyte layer 6 and an electrode (working electrode) 7 made of gold, platinum, silver or carbon paper. The ion-exchange membranes 4, 5, electrolyte layer 6 and electrode 7 are so held by an inner cylinder 8 as to come in contact with the outer cylinder 2 and the ionic medicine-containing substance (or ionic medicine itself). After the use, a proposal has been made concerning the structure of the working electrode part to remove the inner cylinder 8 and to refill the new medicine-containing layer 1 and the new ion-exchange membrane 5.
However, the above-mentioned conventional structure of the working electrode part is complex holding two pieces of ion-exchange members 4 and 5 in contact with the medicine-containing layer 1. Besides, the outer cylinder 2 and the inner cylinder 8 are the housings that must be made of a material having a strength to some extent. Therefore, the iontophoresis device having the above-mentioned electrode structure is produced through cumbersome steps resulting in an increase in the cost of production. Besides, use of a stiff material deteriorates the property of following the surface 3 of the living body. Further, in order that the medicine-containing layer 1 will not leak out during the transit or preservation, it is necessary to provide all of the ion-exchange membrane 5, electrolyte layer 6, electrode 7 and inner cylinder 8 in place, causing, however, the device to become bulky and heavy, and requiring laborious work and cost for transit and preservation. When the medicine-containing layer 1 is to be renewed, further, the outer cylinder 2 and the inner cylinder 8 that need not be replaced must also be transited. Besides, renewal of the medicine-containing layer 1 requires very cumbersome work, which must be improved.